One-Flowered
Broomrape
Orobanche uniflora
Broomrape family (Orobanchaceae)
Description:
This
wildflower is a perennial, producing 1-5 erect flowering stalks about
3-8" tall. The flowering stalks are produced by a scaly short stem that
is 1" or less in length; this stem is usually underground and only the
flowering stalks are visible above ground. The short scales along the
stem are highly modified leaves; they are oval to ovate in shape and
somewhat thick and succulent. The flowering stalks are usually pale
gray or grayish tan, terete, and hairy. At the apex, each stalk
produces a single nodding flower about ¾–1" long. This flower has a
tubular corolla with 5 spreading lobes and a short hairy calyx with 5
lanceolate teeth; the teeth usually have slender tips. The coloration
of the calyx is usually similar to the flowering stalk. The corolla is
white to lilac or a blending of these two colors (rarely is it purple,
at least in the Midwest); it is covered with short fine hairs. Along
the lower throat of the corolla, there is usually a patch of bright
yellow hairs, although sometimes these hairs are cream-colored or
white. Inserted within the corolla, there is an ovary with a single
style and 4 stamens. The blooming period occurs from late spring to
early summer and lasts about 2-4 weeks. In the absence of
cross-pollination by insects, the flowers are self-fertile. Each flower
is replaced by an ovoid seed capsule, that splits open to release
minute seeds. These seeds are small enough to be blown about by the
wind and they eventually sink into the crevices of the soil and ground
litter. The root system is parasitic, developing feeder roots
(haustoria) that attach themselves to the roots of a suitable host
plant. One-Flowered Broomrape is holoparasitic and lacks chlorophyll;
it is dependent on the host plant for nutrients.
Cultivation:
This wildflower is often found in moist rocky areas where there is some
protection from the wind. However, it is also found in non-rocky soil.
The presence of a suitable host plant is required before the seeds will
germinate. The seeds germinate in response to the presence of chemicals
in the soil that the developing host plant produces. In addition, a
suitable fungus may be necessary to function as an intermediary between
the seedling and host plant. Suitable host plants include Sedum
spp. (Sedums), upland Saxifraga spp.
(Saxifrage), Helianthus spp. (Sunflowers), Solidago
spp. (Goldenrods), and probably other plant species.
Transplanted specimens of One-Flowered Broomrape are unlikely to
survive for very long.
Range & Habitat:
One-Flowered Broomrape is occasional in Illinois, except in the SE
section, where it is rare or absent. This is the most common Orobanche
sp. (Broomrape) in the state; it is native. Habitats include
upland
woodlands, rocky cliffs where some seepage occurs, the base of bluffs,
rocky glades, and thickets. This species is usually found in high
quality natural areas.
Faunal Associations:
The flowers are cross-pollinated by bumblebees and possibly other
long-tongued bees. Charles Robertson (1929) observed the bumblebee, Bombus
pensylvanicus, visiting the flowers for nectar. Aside from
this observation, very little appears to be known about floral-faunal
relationships for this species.
Photographic Location:
The photograph (Copyright © 2009) of Orobanche uniflora
was taken by Lisa Culp in a wooded area of Somme Prairie Grove Nature
Preserve in Cook County, Illinois.
Comments:
This unusual wildflower has a reputation of appearing unexpectedly in
one area, only to disappear and reappear in another area of the same
habitat. Most likely, this intermittent pattern results from the
underground stems producing flowering stalks during some years, but not
others. Unlike some other species in this genus, One-Flowered Broomrape
produces only a single flower per stalk, rather than a spike-like stalk
with multiple flowers. Only one other species in Illinois, Orobanche
fasciculata (Clustered Broomrape), shares this
characteristic. Clustered Broomrape has a longer scaly stem (2-4") that
is also underground, from which 4-12 flowering stalks develop above
ground. There is a tendency for the lobes of its flowers to be less
spreading or more divided into 2 lips; One-Flowered Broomrape has
flowers with spreading lobes and poorly defined upper and lower lips.
The common name of this genus, 'Broomrape,' derives from an Orobanche
sp. in Europe that is parasitic on Broom (Cytisus sp.) as a
host plant. Other common names of Orobanche uniflora
are 'Naked Broomrape' and 'Ghost Pipes.'